Presently, there are over one million tractor trailers in operation in the United States. Many of these tractor-trailers are owned by independent owner-operators. Tractor-trailers are subject to extensive federal and state weight regulations. The violation of these weight regulations can result in substantial fines and penalties to the operator or owner. When a tractor-trailer combination is loaded very near to its limit under law, it will frequently be weighed. Under law, the weight of the loaded trailer must be appropriately distributed under a calculation known as the "bridge formula". The bridge formula determines the distribution of weight within the trailer and factors in the distance between the cab and the rear axles of the semi-trailer.
When a truck is stopped on the road for a random weight measurement, it may have too much weight distributed over the rear dual axles. If the weight distribution falls outside the acceptable limits under the bridge formula, the truck will not be permitted to continue until the weight has been properly redistributed. Rather than redistribute the weight within the trailer itself (which would be a monumental task), the operator usually adjusts the weight by moving one or both of the axles of the semi-trailer.
Unfortunately, the movement of the axles when a trailer is fully loaded is itself a considerable and time consuming task. Most semi-trailers comprise a wheeled tandem affixed to a carriage which is slidably adjustable along an apertured track on the trailer and which is retained in position by pins inserted into the apertures.
Presently, the vast majority of trailers are readjusted in the following manner. Initially, the operator, via a hand activated lever or mechanism, removes the pins thus freeing the carriage to be adjusted relative to the trailer bed. After the pins are removed, the rear tandem is locked into place by the application of the brakes. The trailer bed is then slid over the locked dual tandem wheels using the power of vehicle cab. Once the rear tandem is moved into the correct position, the pins are then reinserted by hand back into a different pair of apertures so that the trailer position is locked.
There are several problems associated with this method for readjusting the position of a rear tandem. Initially, this method relies largely upon trial and error before the correct positioning is achieved. Because this method relies upon the power of the vehicle cab to slide the trailer, precise incremental movements of the trailer are not possible. Furthermore, it is frequently difficult to manually remove the pins from the apertures. This may be particularly problematic in cold or inclimate weather. Often the pins may be frozen, locked or rusted into position.
In addition, due to the dangerous nature of this method, there has heretofore been a need to seal off the ends of the tracks, because the trailer could slide completely off the rear tandem as it was pulled or pushed by the vehicle cab. In many trailers, the rearmost two sets of holes are effectively sealed off in order prevent this eventuality, thus limiting the range which the dual tandems can be extended. Finally, this method often leads to "blown" vehicle engines resulting from the large amount of force required to slide the trailer bed over the locked rear wheel tandem.
Various alternative methods have also previously been devised to redistribute the weight of a semi-trailer. U.S. Pat. No. 3,203,711, for example, discloses a floating axle attachment in which a fifth floating axle is slid beneath the semi-trailer. This particular method is expensive and requires a specialized cab and trailer configuration.
Another type of prior art device adjusts the location of the trailer coupling in order to effectuate weight distribution and transfer. See, U.S. Pat. Nos. 2,832,610; 4,662,670; 3,402,944 and 2,153,468. The devices disclosed in these patents are similarly complex and require expensive hydraulic cab configurations. U.S. Pat. No. 2,153,468 discloses a load redistribution system which incorporates a separate trailer dolly which rides on the main trailer bed.
A third type of prior art device is directed to a system which adjusts the length of the chassis or trailer bed. See U.S. Pat. No. 2,371,261. This method is similarly expensive and requires specialized trailer configurations.